Re: Iridium/Point Meteors

Eberst (
Fri, 26 Sep 1997 19:49:55 +0100

At 17:08 97/09/24 EDT, Wayne T Hally wrote:

>	My biggest beef in satellite-land is the Iridium flares, since they 
>resemble what is a rare meteoric event- the point meteor (one coming 
>directly at you...hence no motion).  

On the contrary, Iridium flares do show motion - the orbital motion of the 
satellite at 792 km height, orbiting 14.34217 times/day, which at an elevation
of 50degrees gives an angular velocity of 0.4236 deg/sec. Since the flares
last typically 10-20 seconds, the object will move 4-9 degrees across the sky.
Also point meteors are unlikely to last more than 2 seconds, whereas the Iridium
flares last 5-10 times that duration.

There are, however, other satellites that mimic point meteors much more closely;
the "Midas" satellites for example - 61sigma 1, 61alpha-delta 1, 62kappa 1,
63-30A, 66-77A, 66-89A. These can give isolated, brief but bright flashes which
along with their low angular velocity, will deceive the unwary observer. I would
recommend that the meteor observer always takes a pair of binoculars to a 
meteor-watch, so that the area where any such isolated flashes are seen, can be
immediately inspected with binoculars. In the majority of cases, the culprit 
satellite will be seen crawling away at its more normal magnitude around +8.

best wishes  Russell  Eberst  @   North: 55 degrees, 56 minutes, 55 seconds
             West:  3 degrees, 8 minutes, 18 seconds: 
             43metres (150 feet) above sea-level